In wireless communications networks, antenna design may be key to obtaining good performance and capacity. This applies for the wireless communication from a network node to a wireless user terminal or conversely, as well as between two network nodes.
Multi-antenna techniques are used in cellular wireless communications to improve coverage, capacity, and reliability. Typical base antennas comprise one or more antenna columns along a horizontal direction, where each column typically consists of multiple dual-polarized radiating elements arranged along a vertical direction. These radiating elements are typically combined via a passive feed network to create a narrow elevation beam. Furthermore, a linear phase progression or time delay may be applied over the vertically displaced radiating elements to tilt the elevation beam below the horizon in order to reduce the interference transmitted to adjacent sites. A radio and baseband branch is then typically connected to each polarization on each column, enabling signal processing in the azimuth and polarization domains.
In cellular wireless communications, sectorization can be used to increase the system capacity. Typical deployments use three sectors per site, but in areas where extra high capacity is needed six sectors per site are also used. Sectorization can be achieved by having directive antennas pointing in different directions so that the different sectors become spatially isolated. This can be achieved by mechanically steering directive antennas in the desired directions, by analog or digital beamforming (BF), or by a combination thereof.
The spatial degrees of freedom (DoF) offered by a multi-antenna solution can also be used for user-specific beamforming (UE-specific BF), diversity, and spatial multiplexing to further increase the performance of a system. For a given amount of antenna, radio, and baseband resources there exist trade-offs regarding what the available DoF should be used for. For example, an antenna arrangement could be used for sectorization, UE-specific BF, diversity, and/or spatial multiplexing. Devoting DoF to one of these functions may sacrifice the available DoF for other functions. How the available DoF should be allocated to different functions depends on many aspects and may vary over time and between different sites over a cellular network.
Hence, there is still a need for a flexible antenna arrangement.